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ITKconfig - A small, powerful configuration parser for Golang

Originally started as an internal project at the Student society in Trondheim this package has now been open sourced, as we believe it is the simplest and best way to manage configuration files for Go-projects. It serves its purpose for our projects, but we would love to hear your use-cases and feedback, if any.

Features and core-principles

  • Makes writing Key-Value configuration files easy.
  • Allows, in contrast to JSON, comments in your files - just prepend them with a #.
  • If you want to use # in a value, or preserve leading and trailing spaces, wrap the value in double quotes: "#value"
  • Use the same methods as when demarshalling JSON-files, just define your configuration struct with your wanted types and let ITKconfig take care of the rest.
  • Source code is simple and short, which makes it easy to understand the flow of the program, but also make changes to the library if you like.

Example configuration file

An example scenario is given where you want to provide a configuration file to your Web-application. It could look like:

# Port that the webservice is listening to
Port = 8000

# Folder where we find our templates
TemplatesFolder = templates

# Enable or disable debug mode, giving more output to the user.
Debug = true

# Various contact points for the admins
AdminEmail = foo@mailinator.com
AdminEmail = bar@mailinator.com

Then, provided that this file is called myapp.config we can load it into our application by the following simple code:

package main

import (
  "fmt"
  "github.com/itkinside/itkconfig"
  "log"
)

type Config struct {
  Port            int
  TemplatesFolder string
  Debug           bool
  AdminEmail      []string
}

func main() {
  // Some sane defaults for our project.
  config := &Config{
    Port:            80,
    TemplatesFolder: "temps",
    Debug:           false,
    AdminEmail:      []string{"admin@mailinator.com"},
  }

  // Override (or append on) defaults with config-file.
  err := itkconfig.LoadConfig("myapp.config", config)
  if err != nil {
    log.Fatal(err)
  }

  // Print our variables, just to show off.
  fmt.Printf("Port: %d\n", config.Port)
  fmt.Printf("Templates: %s\n", config.TemplatesFolder)
  fmt.Printf("Debug: %v\n", config.Debug)
  for i, email := range config.AdminEmail {
    fmt.Printf("Admin email %d: %s\n", i, email)
  }
}

Could it be more simple, and yet so powerful?

Some useful tips

Comments

The hash symbol is your friend, and you can use it wherever you want. You may also use it inside a variable by escaping it:

# This is a comment
Key = some value # Also a comment
Foo = "#something" # This is first comment on this line.
Lists of key-values

Often a simple Key => Value mapping is not sufficient, and you want a key mapping to an array of values. This if fully supported and you can define your struct as:

type Config struct {
  Foo []string
  Bar []float64
  Zoo []int
}

And then in your config-file:

Foo = string number one.
Foo = string number two.
Bar = 1.0
Bar = 2.0
Zoo = 1
Zoo = 2

Which, you guessed it, will map to the arrays Foo{"string number one.", "string number two"}, Bar{1.0,2.0} and Zoo{1,2}.

Which types are valid?

At the moment the following types are valid to use when unmarshaling your config-file:

  • String
  • Int, Int8, Int16, Int32 and Int64
  • Uint, Uint8, Uint16, Uint32 and Uint64
  • Float32 and Float64
  • Bool

And every one of those as slices, as well. For type definitions and more details about other types in Golang please refer to their doc on the subject.

Using defaults

There are three parts to parsing and defining a config in your application, given you want to set default values different from those used by Golang.

First you need to define your Config-type. This is done in order to unmarshal correctly. It is an important step for a type-safe language. An example definition looks like:

type Config struct {
  Foo string
}

Second you need to create a default-variable of the type you defined in the previous step.

cfg := &Config{
  Foo: "My default string",
}

As you can see our variable cfg is a pointer to a Config-type. This pointer is passed on to ITKconfig which sets the appropriate fields based on your config file.

Third you use ITKconfig to parse your config-file, validate it and then override your defaults. This is simply done by:

itkconfig.LoadConfig("filename.conf", cfg)

If you have defined a slice-type in your struct the default-slice will not be overwritten, but rather elements from the config-file will be appended on.

Authors

Pull-request, your issues and any feedback is greatly appricated.

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